Using JVM Shutdown Hooks to Kill a Child Process

Today I spent some time writing a runner for a command-line Java socket application. I’d assumed that it would be easy enough to quit the process by hitting ^C. I’m here to report that this is not the case.

Hitting ^C shuts down the JVM, so if you’ve forked a separate Java process it’ll become orphaned.

To get past this you have to implement a shutdown hook, which will run during the JVM shutdown sequence, in effect allowing your application to handle the signal. Which is exactly what I wanted.

Here’s a bit of code:

{% highlight java %} class Runner {

...

public int exec() {
    final String[] args = new String[] {
            "java",
            "-classpath", classpath,
            mainclass
    };
    
    final ProcessBuilder pd = new ProcessBuilder(args);
    pd.directory(new File(workingDirectory, "bin"));
    final Process p = pd.start();
    Runtime.getRuntime().addShutdownHook(new Thread() {

        public void run() {

            p.destroy();
        }
    });
    return p.waitFor();
}

} {% endhighlight %}

The Runtime API is here.